hi, i went on the ocean village last year , it was alright as you did not have to get glammed up, casual clothes at night, i am going on a 3week cruise on the island star in november and thats another casual cruise, it also means you can please yourself when you want to dine.
I've also been on the Ocean Village and enjoyed it. No black tie dinners, just wear what you want (within the laws of decency) and eat when you want. Also, tips are included, which they aren't on many cruise lines.
By 'casual' do you mean 'cheap' as some of the top 5* cruises are casual with no need to 'dress up'.?!? But these do not come under the 'cheap' banner!
Have you looked at www.cruisecritic.com - scroll down till you get to ReadMember Reviews and you will get reviews of pretty nearly every cruise ship [it is an American site so nothing about the 3* Island cruise lines there though]
For a good middle of the road cruise experience I would recommend NCL or RCI - 4* cruises with new ships with loads of things to do on board and a variety of places to eat [and you don't need to dress up if you don't want to!]